Linkage of the long QT syndrome to the short arm of chromosome 11: use of five highly polymorphic markers towards more detailed localization of the mutant gene

The long QT syndrome is an autosomally dominantly inherited cardiac disorder characterized by abnormalities of myocardial repolarization, exercise- or stress-related syncopal attacks and risk of sudden death due to cardiac arrhythmias. Genetic linkage studies have defined three LQT loci on chromosomes 11p15.5, 3q21–24 and 7p35–36. We performed linkage analyses in three Finnish LQT families using five amplifiable markers assigned to chromosome 11p15. By multipoint linkage analyses we obtained a maximal lod score of 5.503, suggesting that the LQT1 locus maps between D11S922 and D11S1338 on chromosome 11. Our data provide a step towards closer definition of the exact borderlines of the LQT1 locus in chromosome 11 and demonstrate markers with high utility in identification of gene carriers in the affected families.     

Fc receptor isoforms exhibit distinct abilities for coated pit localization as a result of cytoplasmic domain heterogeneity

Mouse macrophages and lymphocytes express two distinct isoforms of a single class of Fc receptor for IgG. The macrophage isoform (FcRII-B2) is identical to the lymphocyte isoform (FcRII-B1) except for an inframe insertion in the cytoplasmic tail of FcRII-B1 that increases its length from 47 to 94 amino acids. To determine the functional significance of this cytoplasmic domain variation, presumably the result of alternative mRNA splicing, we expressed both isoforms in receptor-negative fibroblasts. While FcRII-B2 mediated the efficient ligand internalization and delivery to lysosomes, endocytosis via FcRII-B1--and via a tailminus mutant--was relatively inefficient. This difference reflected the inability of FcRII-B1 (and the tailminus mutant) to accumulate in clathrin-coated pits. Thus, the FcRII-B2 cytoplasmic tail contains a domain needed for accumulation in coated pits, and this domain is disrupted by the 47 amino acid insertion in FcRII-B1.     

Serum selenium concentration related to myocardial infarction and fatty acid content of serum lipids.

A longitudinal case-control study of 33 patients with one or more risk factors for coronary heart disease and 64 controls showed that the serum selenium concentration (range 0.63-1.33 mumol/l (50-105 micrograms/l] was not associated with development of clinical manifestations of coronary heart disease during a follow up of five to seven years. The content of polyunsaturated fatty acids, especially eicosapentaenoic acid, in serum cholesterol esters and phospholipids was positively correlated with selenium concentration. As a low content of polyunsaturated fatty acids in serum lipids was an independent risk factor for coronary heart disease in these subjects it may be hypothesised that the high coronary risk in subjects with a very low serum selenium concentration (less than 0.57 mumol/l (less than 45 micrograms/l] might be due not to selenium deficiency but to the coexisting low concentrations of polyunsaturated fatty acids in serum.     

Correlation between serum levels of some cholesterol precursors and activity of HMG-CoA reductase in human liver

The possibility that the serum concentrations of various cholesterol precursors may reflect the activity of the hepatic HMG-CoA reductase was investigated in humans under different conditions. The serum levels of squalene, free and esterified lanosterol, (4 alpha, 4 beta, 14 alpha-trimethyl-5 alpha-cholest-8, 24-dien-3 beta-ol), two dimethylsterols (4 alpha, 4 beta-dimethyl-5 beta-cholest-8-en-3 beta-ol and 4 alpha, 4 beta-dimethyl-5 alpha-cholest-8, 24-dien-3 beta-ol), two methostenols (4 alpha-methyl-5 alpha-cholest-7-en-3 beta-ol and 4 alpha-methyl-5 alpha-cholest-8-en-3 beta-ol), two lathosterols (5 alpha-cholest-7-en-3 beta-ol and 5 alpha-cholest-8-en-3 beta-ol) and desmosterol (cholest-5, 24-dien-3 beta-ol) were measured in untreated patients (n = 7) and patients treated with cholestyramine (QuestranR, 8 g twice daily for 2-3 weeks, n = 5) or chenodeoxycholic acid (15 mg/kg body weight daily for 3-4 weeks, n = 8) prior to elective cholecystectomy. The activity of the hepatic microsomal HMG-CoA reductase was measured in liver biopsies taken in connection with the operation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Decrease of aflatoxin B1 in yoghurt and acidified milks

Fermentation of yoghurt and acidified milks containing aflatoxin B₁ (AB₁) were studied. AB₁ added to milk before fermentation at concentrations of 600, 1000 and 1400 g/kg was reduced in yoghurts (pH 4.0) by 97, 91 and 90%, respectively. Coagulation time was approximately the same as in the controls. Streptococci had longer chains than those in the controls. The main decrease of AB₁ occurred during the milk fermentation. A decrease of AB₁ (conc. 1000 g/kg) in milks acidified with citric, lactic and acetic acids (pH 4.0) was 90, 84 and 73%, respectively.     

Distinct Muscle Biopsy Findings in Genetically Defined Adult-Onset Motor Neuron Disorders

The objective of this study was to characterize and compare muscle histopathological findings in 3 different genetic motor neuron disorders. We retrospectively re-assessed muscle biopsy findings in 23 patients with autosomal dominant lower motor neuron disease caused by p.G66V mutation in CHCHD10 (SMAJ), 10 X-linked spinal and bulbar muscular atrophy (SBMA) and 11 autosomal dominant c9orf72-mutated amyotrophic lateral sclerosis (c9ALS) patients. Distinct large fiber type grouping consisting of non-atrophic type IIA muscle fibers were 100% specific for the late-onset spinal muscular atrophies (SMAJ and SBMA) and were never observed in c9ALS. Common, but less specific findings included small groups of highly atrophic rounded type IIA fibers in SMAJ/SBMA, whereas in c9ALS, small group atrophies consisting of small-caliber angular fibers involving both fiber types were more characteristic. We also show that in the 2 slowly progressive motor neuron disorders (SMAJ and SBMA) the initial neurogenic features are often confused with considerable secondary “myopathic” changes at later disease stages, such as rimmed vacuoles, myofibrillar aggregates and numerous fibers reactive for fetal myosin heavy chain (dMyHC) antibodies. Based on our findings, muscle biopsy may be valuable in the diagnostic work-up of suspected motor neuron disorders in order to avoid a false ALS diagnosis in patients without clear findings of upper motor neuron lesions.     

Issues affecting molecular staging in the management of patients with melanoma

Prediction of metastatic potential remains one of the main goals to be pursued in order to better assess the risk subgroups of patients with melanoma. Detection of occult melanoma cells in peripheral blood (circulating metastatic cells [CMC]) or in sentinel lymph nodes (sentinel node metastatic cells [SNMC]), could significantly contribute to better predict survival in melanoma patients. An overview of the numerous published studies indicate the existence of several drawbacks about either the reliability of the approaches for identification of occult melanoma cells or the clinical value of CMC and SNMC as prognostic factors among melanoma patients. In this sense, characterization of the molecular mechanisms involved in development and progression of melanoma (referred to as melanomagenesis) could contribute to better classify the different subsets of melanoma patients. Increasing evidence suggest that melanoma develops as a result of accumulated abnormalities in genetic pathways within the melanocytic lineage. The different molecular mechanisms may have separate roles or cooperate during all evolutionary phases of melanocytic tumourigenesis, generating different subsets of melanoma patients with distinct aggressiveness, clinical behaviour, and response to therapy. All these features associated with either the dissemination of occult metastatic cells or the melanomagenesis might be useful to adequately manage the melanoma patients with different prognosis as well as to better address the different melanoma subsets toward more appropriate therapeutic approaches.     

Overexpression of spermidine/spermine N 1-acetyltransferase or treatment with N 1-N 11-diethylnorspermine attenuates the severity of zinc-induced pancreatitis in mouse

Depletion of pancreatic intracellular polyamine pools has been observed in acute pancreatitis both in the animal models and in humans. In this study, the wild-type mice, polyamine catabolic enzyme spermidine/spermine N(1)-acetyltransferase overexpressing (SSAT mice) and SSAT-deficient mice were used to characterize the new zinc-induced acute pancreatitis mouse model and study the role of polyamines and polyamine catabolism in this model. Intraperitoneal zinc injection induced acute necrotizing pancreatitis in wild-type mice as well as in SSAT-overexpressing and SSAT-deficient mice. Serum α-amylase activity was significantly increased in all zinc-treated mice compared with the untreated controls. However, the α-amylase activities in SSAT mice were constantly lower than those in the other groups. Histopathological examination of pancreatic tissue revealed edema, acinar cell necrosis and necrotizing inflammation, typical for acute pancreatitis. Compared with the other zinc-treated mice less damage according to the histopathological analysis was observed in the pancreatic tissue of SSAT mice. Levels of intracellular spermidine, and occasionally spermine, were significantly decreased in pancreases of all zinc-treated animals and SSAT enzyme activity was enhanced both in wild-type and SSAT mice. Interestingly, a spermine analog, N(1), N(11)-diethylnorspermine (DENSpm), enhanced the proliferation of pancreatic cells and reduced the severity of zinc-induced pancreatitis in wild-type mice. The results show that in mice a single intraperitoneal zinc injection causes acute necrotizing pancreatitis accompanied by decrease of intracellular polyamine pools. The study supports the important role of polyamines for the integrity and function of the pancreas. In addition, the study suggests that whole body overexpression of SSAT obtained in SSAT mice reduces inflammatory pancreatic cell injury.     

The p53 Tumor Suppressor Causes Congenital Malformations in Rpl24-Deficient Mice and Promotes Their Survival

Hypomorphic mutation in one allele of ribosomal protein l24 gene (Rpl24) is responsible for the Belly Spot and Tail (Bst) mouse, which suffers from defects of the eye, skeleton, and coat pigmentation. It has been hypothesized that these pathological manifestations result exclusively from faulty protein synthesis. We demonstrate here that upregulation of the p53 tumor suppressor during the restricted period of embryonic development significantly contributes to the Bst phenotype. However, in the absence of p53 a large majority of Rpl24^Bst/+ embryos die. We showed that p53 promotes survival of these mice via p21-dependent mechanism. Our results imply that activation of a p53-dependent checkpoint mechanism in response to various ribosomal protein deficiencies might also play a role in the pathogenesis of congenital malformations in humans.Nascent ribosome biogenesis is required during cell growth, proliferation and differentiation (42, 47). It is temporally and spatially organized within the nucleolus, where rRNAs are transcribed, processed, modified, and assembled with ribosomal proteins (RPS) to generate the mature 40S and 60S ribosomal subunits (13). RPS participate in additional steps in ribosome biogenesis in the nucleoplasm and the cytoplasm, such as the transport of ribosomal precursors, stabilization of ribosome structure, and regulation of different steps in protein synthesis (15).The critical role of at least some RPS in mammals is underscored by the pathological or lethal consequences of the deficiency of just one allele. Only a few heterozygous mutations of RP genes have been shown to be viable in mammals, and each of them has shown a relatively specific phenotype. Germ line heterozygous mutation for RPS19, RPS24, RPS17, RPL35a, RPL5, and RPL11 genes have been found in patients with Diamond-Blackfan anemia, which is characterized by absent or decreased erythropoiesis, and less frequently by small stature and various somatic malformations that mostly occur in the cephalic region, as well as an increased incidence of leukemia, osteogenic sarcoma, and myelodisplastic syndrome (7, 9, 12, 17, 18). Recently, a link between heterozygous mutations in Rps19 and Rps20 and dark skin phenotype in mice has been demonstrated (29).Another heterozygous RP mutant is the Belly Spot and Tail (Bst) mouse (34). This is a semidominant, hypomorphic mutation caused by an intronic deletion in the Rpl24 gene, affecting Rpl24 mRNA splicing. Rpl24^Bst/+ mice are characterized by reduced body size, a white ventral middle spot, white hind feet, retinal abnormalities, a kinked tail, and other skeletal abnormalities. Since Rpl24^Bst/+ mouse embryonic fibroblasts from these mice showed a significant reduction in the rate of overall protein synthesis, it has been suggested that their phenotype result exclusively from faulty translation of mRNAs in tissues that depend on rapid and flawless protein synthesis (34).It has been argued that the differential phenotypes of heterozygous mutants of RP genes in mammals might be attributable to the expression levels of the respective RP and the consequent decrease in the amount of ribosomes, impairment of specific steps in protein synthesis, and potential extraribosomal function. However, it should be pointed out that the relative contribution of the impaired protein synthesis or extraribosomal function to these phenotypes remains to be determined (9, 17, 34, 36, 37, 43, 57).Recent evidence indicates that deficiencies in individual RPS could lead to pathological consequences via activation of a p53-dependent checkpoint regulatory mechanism. We demonstrated that inducible deletion of the Rps6 gene in the liver of adult mice inhibits the synthesis of the 40S ribosomal subunit, as well as proliferation of liver cells, after partial hepatectomy, despite seemingly unaffected protein synthesis (54). These observations suggested the existence of a novel checkpoint, downstream of the deficiency in ribosome biogenesis. Likewise, the perigastrulation lethality of Rps6 heterozygote embryos appears to reflect the triggering of a p53-dependent checkpoint response rather than a deficit in protein synthesis (37). We have assumed that activation of a p53-dependent checkpoint is triggered by impaired rRNA processing in the nucleolus in Rps6-deficient cells, since the nucleolar structure and function are compromised by almost all known p53-inducing stresses (37, 41, 50). Based on all of these observations, it could be speculated that the rare occurrence of RP heterozygosity in mammals reflects the fatal consequences of p53-dependent checkpoint activation (36, 37). In addition to function in development, this checkpoint may also play a role in other processes. Since various RP deficiencies in Drosophila melanogaster, zebrafish, and humans pose a great risk for development of malignant tumors, it is possible that induction of a p53-dependent checkpoint response prevents expansion of such potentially hazardous cells (1, 9, 11, 56).Recently, we initiated an RNA interference screen for RP deficiencies that upregulate the p53 tumor suppressor in A549 cells. It has been previously suggested that a defect in ribosome biogenesis in the nucleolus caused by a RP deficiency triggers the p53 response (36, 37, 50). A number of studies in yeast showed that Rpl24 does not participate in ribosome biogenesis in the nucleolus, but it assembles late with the nascent 60S ribosomes in the cytoplasm and regulates the 60S subunit joining step during translation initiation and other steps in protein synthesis (10, 25, 45). Thus, it was surprising to observe that RPL24 deficiency triggered the p53 response in our screen. This observation led us to consider the possibility that p53 is upregulated in Rpl24^Bst/+ mice. In contrast to previous opinion that the phenotype of these mice results exclusively from impaired protein synthesis (34), we demonstrate here that it is largely caused by the aberrant upregulation of p53 protein expression during embryonic development.     

Harmonization is more important than experience—results of the first Nordic–Baltic diatom intercalibration exercise 2007 (stream monitoring)

The goal of this study was a harmonization of diatom identification and counting among diatomists from the Scandinavian and Baltic countries to improve the comparison of diatom studies in this geographical area. An analysis of the results of 25 diatomists following the European standard EN 14407 during an intercalibration exercise showed that a high similarity was achieved by harmonization and not because of a long experience with diatoms. Sources of error were wrong calibration scales, overlooking of small taxa, especially small Navicula s.l., misidentifications (Eunotia rhomboidea was mistaken for Eunotia incisa) and unclear separation between certain taxa in the identification literature. The latter was discussed during a workshop with focus on the Achnanthes minutissima group, the separation of Fragilaria capucina var. gracilis from F. capucina var. rumpens, and Nitzschia palea var. palea from N. palea var. debilis. The exercise showed also that the Swedish standard diatom method tested here worked fine with acceptable error for the indices IPS (Indice de Polluo-sensibilité Spécifique) and ACID (ACidity Index for Diatoms) when diatomists with a low similarity (Bray–Curtis <60%) with the auditor in at least one of the samples are excluded.